Glyphosate is used to kill unwanted plants (weeds) in
crop fields, amenity areas and home gardens, and on a
global scale it has become the most widely used
pesticide(1). The manufacturers of glyphosate-based
herbicides claim their ‘low toxicity and environmental
friendliness’(2). However, recent independent research
indicates that glyphosate may not be as safe as
Glyphosate, sold most widely under the trade name
Roundup, is applied as a herbicide both after the crop
has germinated (post-emergent use) and before seeding
(pre-emergent use in low-tillage cultivation). It acts
non-selectively, killing a broad spectrum of plants
including grasses, perennials and woody plants(3).
Glyphosate is absorbed through the leaves and is then
transported throughout the plant. It inhibits a
metabolic pathway required to form essential amino acids
that exist in plants and microorganisms but not in
animals(4). Glyphosate is an organophosphonate or salt
of a phosphonic acid. It does not inhibit activity of
the enzyme acetylcholinesterase (as do organophosphates)
that is crucial for transmission of nerve signals in
animals and insects(5).
Since its introduction during
the mid-seventies, use of glyphosate has increased
rapidly(6). In the USA in the years 1997 and 2002 it was
among the five most used active ingredients, and
second-most used by homeowners and the government or
industry(7,8). The recent increase in use is largely due
to the introduction of genetically modified (GM)
glyphosate-tolerant crops, for example GM soybean in
Argentina(9). Expansion in practice of low-tillage has
also increased its use(10). Worldwide sales of
glyphosate-based products exceeded US$3,000 million in
2002 and the main manufacturer Monsanto expects an
increase in 2004 due to increased sales of their
products (including ‘Roundup’) in Brazil(11,12).
Formulations of products based on glyphosate
herbicides are formulated with one or more surfactants.
The surfactant spreads the solution across the leaf,
penetrates the leaf and enhances the uptake of
glyphosate by the plant(13). A class of surfactants
known as polyoxyethylene tallowamines (POEA) are used
most frequently. These are mixtures of ethoxylated
long-chain alkyl amines derived from fatty acids from
animals(14) or tall oil (resin from pine wood)(15).
Proportions of glyphosate and surfactant have not
changed in many products over the last few years
(manufacturers material safety data sheets)(16) and
despite health concerns POEAs continue to be used, for
example in ‘Roundup Ultra’(17). Other surfactants are
also used, such as alcohol ethers and fatty acid
esters18, or biodegradable rapeseed oil derivatives(19).
Some glyphosate-based herbicide formulations contain a
second active ingredient as several weeds have become
resistant to glyphosate(20).
Acute toxicities of glyphosate-based herbicides
Acute toxicity refers to the
immediate effects (0-7 days) of exposure to a substance.
The US EPA ranks glyphosate in toxicity category III
(these products bear the label: ‘Caution’)(21). However,
some glyphosate formulations are in toxicity category I
(‘Danger’) or II (‘Warning’) for primary eye irritation
or skin irritation(22). Glyphosate is categorised by the
World Health Organisation (WHO) in acute toxicity class
U: ‘Product unlikely to present acute hazard in normal
use’(23). Formulated products with a surfactant are
either in WHO class U or in class III (‘Slightly
Hazardous’)(24). Glyphosate was found to be irritating
to the eyes and slightly irritating to the skin when
tested on rabbits(25), while a Monsanto safety sheet
says a formulation similar to ‘Roundup Original’ (41%
glyphosate isopropylammonium salt, 8% surfactant and 51%
water, by weight) caused severe eye irritation and
destruction of eye tissue requiring more than 21 days to
heal when tested on rabbits(26). Tests on rats revealed
that formulations containing glyphosate and a POEA
surfactant caused more severe respiratory effects and
damage to lung tissue than glyphosate on its own(27),
and POEA accounted for a major part of the toxicity of
the product Roundup to different aquatic organisms(28).
of farm workers to smaller amounts of Roundup, for
example by rubbing in an eye, is reported to have caused
swelling of the eye and lid, rapid heartbeat and
elevated blood pressure, or swelling of the face, due to
residues transferred from the hands after touching leaky
equipment, while accidental drenching caused eczema of
the hands and arms which lasted two months(29). A safety
evaluation concluded ‘that under present and expected
conditions of use, Roundup does not pose a health risk
to humans’(30). However, a case of acute toxic
pneumonitis after inhalation of vapors and air-borne
droplets containing glyphosate has been diagnosed, based
on clinical evidence(31). In another case, inhalation of
a mixture of glyphosate (isopropylamine salt) and the
herbicide butafenacil (WHO class: not listed) led to
high fever and general fatigue immediately
afterwards(32). In 2002 in California, glyphosate
accounted for systemic and respiratory health effects in
four definite/probable and eight possible cases, and for
effects involving only the eyes and/or skin in five
definite/probable and two possible cases among
agricultural workers(33). From 24 people in Denmark who
were exposed to glyphosate by inhalation and from 42
exposed by topical contact, about three quarters
developed poisoning symptoms, mostly related to the
mouth, gastrointestinal tract and the airways(34). In
the UK glyphosate has been the most frequent cause of
complaints and poisoning incidents recorded in recent
years by the Health and Safety Executive’s Pesticides
Incidents Appraisal Panel (PIAP)(35). Aerial spraying of
large areas in Colombia to eradicate cocoa and poppy
crops has caused poisoning in over 4,000 people and very
many animals in one area, and health impacts among over
35,000 indigenous people(36).
Prolonged exposure to glyphosate and chronic toxicity
Rats that had inhaled aerosols
of one-third diluted ‘Roundup’ over several days showed
irritations to the nose tissue, trachea and lungs(37).
Relatively high dose of glyphosate applied to the skin
of rabbits caused a slight degree of dermal irritation,
while a much smaller amount of a formulated product
caused skin irritation that required four weeks to
heal(38). In rats and mice dietary exposure to
glyphosate over three months caused lesions of the
cultures of nerve cells previously exposed to the
insecticide diazinon for two months, toxic effects of
glyphosate appeared at a concentration several times
lower than in non-exposed cells(40). The incidence of
neurologic developmental effects increased more than
threefold among children born to farmers in the US who
used glyphosate(41). Roundup has been found to inhibit
the production of steroid hormones and this may result
in loss of fertility in men(42).
tadpoles, glyphosate was seen to cause DNA damage(43). A
study in the USA found that when farmers used several
individual pesticides, including glyphosate, this was
‘associated with increased Non-Hodgin’s lymphoma (NHL)
incidence’(44). NHL is a malignant tumor of lymphoid
tissue, and a significant association in the incidence
of NHL and exposure to glyphosate has been observed in
Sweden(45). Studies on effects of different
concentrations of glyphosate on chromosome aberrations
and chromatid exchange in human and bovine white blood
cells revealed ‘a dose-related increase in the percent
of aberrant cells’(46), suggesting that ‘either
oxidative stress or a mutagenic effect’(47) is induced.
Environmental fate and ecological impact of glyphosate
In formulated products POEAs
were found to be more toxic than other surfactants and –
when used according to label recommendations under
normal use conditions – could be lethal to bluegill
sunfish in very shallow water (less than 10 cm
depth)(48). Exposure of tadpoles to low concentrations
of glyphosate formulation for a short time revealed
sublethal effects and led to significant mortality(49).
Indirect effects of cereal herbicides including
glyphosate are associated with the decline of 11 bird
species in the UK(50).
Degradation of glyphosate in soil was found to be
slow(51). A study in Denmark has found that:
‘glyphosate, when applied in late autumn, can leach
through the root zone [1m below ground soil] at
unacceptable concentrations in loamy soil’; average
concentrations exceeded the European Drinking Water
Standard (0.1 µg/l) at two sites for glyphosate, and at
one for aminoethylphosphonic acid, a degradation product
detected over one and a half years after
application(52). The Danish government has proposed to
restrict the use of glyphosate, preventing its use
during the autumn and winter on clay soils where the
risk of leaching is high within heavy rainfall. The
restriction is due to come into force in 2004.
It is often argued that glyphosate is an alternative
to the use of herbicides with higher acute toxicities,
such as 2,4-D or paraquat. However, there exists
sufficient evidence that glyphosate can cause harmful
chronic effects to health, and the Danish study on
surface waters revealed an unforeseen way of behaviour
in the environment. The use of glyphosate should be
reduced substantially, especially in developing
countries, to minimise acute and chronic effects on
wildlife and human health.
This factsheet written
by Richard Isenring is an update of a previous version:
PN 33, September 1996, p28-29.
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[This article first appeared
in Pesticides News No. 64, June 2004, pages 20-21